1. Field of the Invention
The present invention relates to a magnetoresistive effect element which detects magnetism by passing a sense current in a direction perpendicular to a film plane of a magnetoresistive effect film, a magnetic head and a magnetic recording/reproducing apparatus.
2. Description of the Related Art
In recent years, hard disk drives (HDDS) have rapidly moved to downsizing and high densities, and are still expected to be higher in density hereafter. High densification of HDD can be realized by increasing the track density by narrowing the recording track width. However, if the track width becomes narrow, intensity of recorded magnetization, namely, a recording signal becomes small, and it is necessary to enhance reproducing sensitivity of an MR head which reproduces a medium signal.
Recently, a GMR head including a highly sensitive spin-valve film using a giant magneto-resistance effect (GMR) has been adopted. The spin-valve film (also called “a spin-dependent scattering unit”) is a multi-layered film having a sandwich structure sandwiching a nonmagnetic spacer layer between two ferromagnetic layers. A magnetization direction of one ferromagnetic layer (called “a pinned layer” or “fixed magnetization layer”) of the two ferromagnetic layers is fixed with an antiferromagnetic layer or the like. A magnetization direction of the other ferromagnetic layer (called “a free layer” or “a free magnetization layer”) is changeable in accordance with an external magnetic field. In the spin-valve film, a large magnetoresistive effect is obtained by a change in a relative angle of the magnetization directions of the two ferromagnetic layers.
A GMR head of a conventional spin-valve film has a CIP (Current in plane) structure which passes a sense current parallel with a film plane (CIP-GMR element). On the other hand, a GMR element of a CPP (Current Perpendicular to Plane) structure (CPP-GMR element) which passes a sense current perpendicularly to a film plane attracts attention since it has a larger GMR effect than the CIP-GMR element.
However, in the case of a spin-valve film structure which is the highest in realizability as a device, the total film thickness of the pinned layer/the nonmagnetic spacer layer/the free layer (spin-dependent scattering unit) which are the layers dependent on spin is very thin, with the small number of interfaces, and therefore, the element resistance when a current is passed perpendicularly in the CPP-GMR element is very small. As a result, the obtained resistance change amount, namely, output is small, though the magnetoresistive effect itself is gigantic. In order to put the CPP-GMR element of the spin-valve film structure into practice, it is important to increase the resistance value of the spin-dependent scattering unit and make the resistance change amount large. Further, it is important to use a material with a large spin-dependent scattering effect for the magnetic material of the pinned layer and the free layer.
It is confirmed that in the metal CPP-GMR element in which all of the pinned layer/the nonmagnetic spacer layer/the free layer (spin-dependent scattering unit) are composed of metal, the spin-dependent interface scattering effect increases by changing the magnetic material of the free layer and the pinned layer to Fe50Co50 of the bcc structure from the conventional Co10Fe10 of the fcc structure, and the spin-dependent bulk scattering effect increases by inserting a extra thin Cu into the magnetic layer. (See, for example, J. Appl. Phys., 92, 2646 (2002), J. Appl. Phys., 93, 7915 (2003)). However The values of the resistance change amount dRA and MR rate of change are still insufficient with respect to the performance required at 200 Gbpsi or more.
Meanwhile, in order to increase the resistance value of the spin-dependent scattering unit of the CPP-GMR element, a CPP-GMR element in which an oxide layer (NOL: Nano Oxide Layer) including a current path (CCP: Current-Confined-Path) in a direction perpendicular to film plane is used for a nonmagnetic spacer layer is proposed (see, for example, JP-A 2002-208744 (KOKAI)). Such an element will be called a CCP-CPP element hereinafter. In the CCP-CPP element, the resistance value of the spin-dependent scattering unit is increased and the resistance change amount can be increased, by the current-confined-path effect of passing a current into only a current path portion, and passing no current to the other portions.
In the CCP-GMR element, the ratio of the CCP-NOL portion is high in the total resistance when a current is passed perpendicularly, and therefore, the area resistance RA and the resistance change amount RA of the CCP-GMR element are determined substantially in the vicinity of the CCP-NOL spacer. Therefore, of the spin-dependent scattering, the interface scattering effect has a larger influence than the bulk scattering effect. Namely, in the CCP-CPP element, it is effective for realizing a high MR change of rate to use a material having a large spin-dependent interface scattering effect as the magnetic layer material of the free layer and the pinned layer.
By using Fe50Co50 of the bcc structure, which has been already confirmed to have a large spin-dependent interface scattering effect in the metal CCP-CPP element, as the magnetic layer of the free layer and the pinned layer of the CCP-CPP element, high resistance change amount and MR rate of change are confirmed (see Appl. Phys. Lett., 87, 082507 (2005)).
The art of suppressing and restoring deterioration of crystallinity by providing a cap layer composed of an element with a large distance between atoms in the closest proximity on the free layer is disclosed (see JP-A 2005-259976 (KOKAI)). In the aforementioned JP-A 2002-208744 (KOKAI), the art of providing a resistance control layer in at least any one of the pinned layer, the free layer and the nonmagnetic intermediate layer is disclosed.